The present invention concerns centrifugal processing apparatus, and more particularly, apparatus that is aerodynamically constructed to provide reduced wind resistance and which enables an efficient drive mechanism.
Centrifugal processing systems are used in many fields. In one important field of use, a liquid having a suspended mass therein is subjected to centrifugal forces to obtain separation of the suspended mass.
As a more specific example, although no limitation is intended herein, in recent years the long term storage of human blood has been accomplished by separating out the plasma component of the blood and freezing the remaining red blood cell component in a liquid medium, such as glycerol. Prior to use, the glycerolized red blood cells are thawed and pumped into the centrifugating wash chamber of a centrifugal liquid processing apparatus. While the red blood cells are being held in place by centrifugation, they are washed with a saline solution which displaces the glycerol preservative. The resulting reconstituted blood is then removed from the wash chamber and packaged for use.
The aforementioned blood conditioning process, like other processes wherein a liquid is caused to flow through a suspended mass under centrifugation, necessitates the transfer of solution into and out of the rotating wash chamber while the chamber is in motion. Thus while glycerolized red blood cell and saline solution are passed into the wash chamber, waste and reconstituted blood solutions are passed from the chamber. To avoid contamination of these solutions, or exposure of persons involved in the processing operation to the solutions, the transfer operations are preferably carried out within a sealed flow system.
One type of centrifugal processing system which is well adapted for the aforementioned blood conditioning process uses the principle of operation described in Dale A. Adams U.S. Pat. No. 3,586,413. The apparatus of the Adams patent establishes fluid communication between a rotating chamber and stationary reservoirs through a flexible interconnecting umbilical cord without the use of rotating seals, which are expensive to manufacture and which add the possibility of contamination of the fluid being processed.
The primary embodiment of the Adams patent comprises a rotating platform which is supported above a stationary surface by meams of a rotating support. A tube is connected to the stationary support along the axis of the rotating platform and the rotating support, with the tube extending through the rotating support and having one end fastened to the axis of the rotating platform. A motor drive is provided to drive both the rotating platform and the rotating support in the same relative direction at speeds in the ratio of 2:1, respectively. It has been found that by maintaining this speed ratio, the tube will be prevented from becoming twisted. An improvement with respect to this principle of operation, comprising a novel drive system for a centrifugal liquid processing system, is disclosed in Khoja, et al. U.S. Pat. No. 3,986,442. In the Khoja, et al. patent, a novel drive system is provided for driving a rotor assembly at a first speed and a rotor drive assembly at one-half the first speed, in order to prevent an umbilical tube from becoming twisted.
While the Adams patent broadly suggests driving the rotating support to allow the tube to provide the necessary torque for driving the rotating platform, it has been discovered that this tube drive principle can be utilized with centrifugal processing apparatus by employing an umbilical tube formed of tubular material having a dynamic stiffness between 0.1 in. .sup.2 pounds and 100 in. .sup.2 pounds. In this manner, the processing chamber forms an idling member which does not require a direct drive by any external device or gears from the primary motor-shaft drive system.
Thus by using a stiff tubular material for the umbilical tube, the processing chamber will follow the driving rotation of such tube to automatically rotate at twice the speed of the tube. The advantage of a non-twisting tube will be maintained with the internal complexity of the centrifuge processing apparatus being significantly reduced. As a further result, the reduction in drive components greatly reduces cleaning requirements and simplifies the loading of software.
It has also been discovered that tubing having superior characteristics for performing with the apparatus rotating at high speeds comprises polyester elastomer. Excellent results have been obtained with tubing comprising a polyester copolymer based on a poly(oxyalkylene), a dicarboxylic acid and a low molecular weight diol. In particular, HYTREL.RTM. 5556, sold by The DuPont Company, has been found to be an effective tubing material, permitting the centrifuge apparatus of the present invention to rotate at high speeds without failure problems concomitant with certain other materials.
This polyester elastomer material used for the tubing segment that is rotated is able to withstand the significant tensile loads resulting from operation at high speeds, the cyclic bending stresses which occur many times per second and the cyclic torsional loading which may be present.
It is, therefore, an object of the present invention to provide centrifugal processing apparatus having flexible umbilical cable segment capable of withstanding the loads and stresses resulting from the operation of the apparatus.
The use of polyester elastomer tubing, particularly HYTREL.RTM. 5556 polyester elastomer, permits the employment of a single tube with multiple fluid pathways, which is desirable in blood centrifugation. This polyester elastomer tubing can be run in the apparatus for extended time periods without cooling fluid flow, in view of its relatively low dynamic loss modulus. Further, this polyester elastomer tubing can be rotated in the apparatus without the necessity for a guide pipe surrounding the tubing, without significant distention. Additionally, the tubing can be used in a tube-drive type system to propel the processing chamber at speeds up to and in excess of 3,000 rpm.
Further advantages of the polyester elastomer tubing are that no protective sheathing is required over the tubing and the material is susceptible to RF welding and can be RF sealed to the vinyl formulation. Of significance in blood processing is the fact that extracts of the material have shown no acute toxicological effects.
It has also been discovered that an efficient drive system can be provided by rendering the centrifugal processing apparatus aerodynamically sound. In an effort to reduce wind resistance, the processing chamber is surrounded by an outer enclosure located between the processing chamber and the umbilical tube. The outer enclosure enables the system to be constructed with smaller and less expensive driving components and also is operable to prevent the tubing from contacting the processing chamber during rotation thereof.
It is, therefore, an object of the present invention to provide centrifugal processing apparatus utilizing aerodynamic principles to provide reduced wind resistance.
A further object of the present invention is to provide centrifugal processing apparatus employing means for preventing the tube from contacting the processing chamber during rotation.
Another object of the present invention is to provide a centrifugal processing apparatus which is simplified in construction and is efficient to manufacture.
Other objects and advantages of the present invention will become apparent as the description proceeds.